Forging aluminum alloy



Patented Sept. 19 1950 FORGING ALUMINUM ALLOY Horace Campbell Hall, Littleoye'r, Harold Ernest Gresham, Little Eaton, near Derby, and William Michael Doyle and Clifford Wilson, Slough, England, assignors to Rolls-Royce Limited, Derby, England, a British company, and High Duty Alloys Limited, Slough,.England, a British company No Drawing. Application January 10, 1949, Serial No. 70,146. In Great Britain January 23, 1948 Thisinvention is for a new and. improved way of producingwrought articles of aluminium alloy especially parts of internal combustion engines which have to resist high stresses at high temperatures.

It is known that silicon considerably facilitates the production of sound castings of aluminium alloys of the type which include copper, magnesium, nickel and iron.

Where an ingot must be cast in order to make the article in question especially a large ingot it is particularly desirable that blow holes and shrinkage cavities are to be avoided and a sound casting produced.

It is good foundry practice therefore to include at least 0.5 per cent of silicon to ensure a good casting.

We have found that the presence of silicon of this amount and more is however disadvantageous when the alloy is to be used at high temperatures, i. e. temperatures of the order of 200C. and upwards. If, however, the alloy hereinafter described is to be produced by the ordinary chill cast or die cast methods silicon of the order of 0.5 per cent at least must be included to make casting practicable.

We have discovered that it is possible to make satisfactory forgings which have a low'percentage of silicon and which achieve desirable properties at high temperature and to do so by initially se-' lccting the elements of the alloy within narrow limits, casting the alloy in a special manner and giving it a particular heat treatment.

We have also found that articles made in this way have improved properties at room temperature.

According to this invention we make a forged article of aluminium base alloy by formin the alloy with the elements in the respective quantities hereunder mentioned, casting the ingot by the direct chill casting process, forging the same to the shape desired, and subjecting the same to the undermentioned heat treatment.

By forgingwe include any method of plastic deformation whether carried out hot or cold. If any considerable plastic deformation is required the process would be" carried out at an elevated temperature.

The alloy is compounded of aluminium and'the 3 Claims. (Cl. 148-325) 2 following elements in the following proportions:

Per cent Copper 1.8to 2.5 Magnesium 1.2 to 2.0 Nickel 0.8 to 1.5 Iron 0.85 to 1.5

(but so that the combined content of iron and nickel does not exceed 2.75 per cent) Silicon 0 to 0.4 Titanium 0.02 to 0.2

Niobium, cerium, beryllium, zirconium, antimony, manganese, molybdenum, chromium, vanadium, zinc, cobalt and silver may be added up to 0.5 per cent each, but not more than 1.5 per cent in total. The content of cobalt may be increased above 0.5 per cent up to 1 per cent if the nickel or the iron is correspondingly reduced and the content of the silver above 0.5 per cent up to 1 per cent if the copper is correspondingly reduced. In each of which cases, the above mentioned maximum of 1.5 per cent may be correspondingly exceeded.

Calcium, barium and strontium should not be present in a total amount of more than 0.2 per cent. One or more of the following elements may be present up to a maximum of 0.1 per cent total: tin, arsenic, bismuth, cadmium, boron, lithium, sodium and potassium.

The heat treatment is to give solution treatment at 525 to 545 C. for from 2 to 30 hours, to quench and to age from C. to 250 C. for from lto 30 hours. Quenching in boiling water may be advantageous.

This invention is particularly suitable for making parts of internal combustion engines which are of comparatively large size and are subject to stresses at high temperatures such as supercharger rotors of internal combustion engines of both the turbine and piston type, and pistons of the latter type of engine.

The alloy is particularly suitable for supercharger rotors of internal combustion turbines which are hot at their extremities but not at the centre where the stresses are highest.

The casting of the alloy is carried out by the direct chill casting process which may. be either the continuous or semi-continuous process. In both ofthese processes, the molten metal is continuously poured at a controlled rate and temperature into a shallow water-cooled mould or die, where solidification commences. The die is of the required peripheral shape. At the same time, the ingot is continuously withdrawn through the bottom of the die, where the solidification is completed by jets of water or by immersion of the ingot in a tank full of water. In the continuous process, arrangements are made by means of a flying saw, or intermediate salt layers, or by interposed sheets of asbestos, or other suitable material, to separate the cast form into the desired ingot lengths, while the ingot is being continuously cast. On the other hand, the casting is intermittent in the case of the semicontinuous process. When the required ingot length has been cast, the pouring is temporarily suspended while the cast ingot is being removed.

Two alloys have been tested to show the comparative advantages of an alloy according to this invention.

Alloy A was formed according to this invention and was of the following composition:

Per cent Copper 2.1 to 2.3 Magnesium 1.5 to 1.7 Nickel 1.2 to 1.4 Iron 1.0 to 1.3 Silicon 0.15 to 0.2 Titanium About 0.06

Alloy B was of the same composition but included silicon from 0.8 to 1.0 per cent.

Alloy A was produced by the semi-continuous casting process, forged and heat treated for 20 Results of tensile tests Alloy A Alloy B Tons per sq. Tons per sq. Cold: in. in.

Max. Stress 28. 7 27. 2 0.1% Proof Stress 21. 6 '19. 1 Hot, tested at 300 C. after 1 hour at temperature:

Max. Stress 10.3 9.6 0.2% Proof Stress 9.4 8.5 Hot, tested at300 C. after 100 hours at temperature:

Max. Stress 6. 5.1 0.2% Proof Stress 4.6 3. 9 Hot, tested at 350 0. after 1 hour at temperature: 7 Max. Stress. 5.6 4.5 0.2% Proof Stress 5.0 3. 4 Hot, tested at 350 0. after 100 hours at temperature:

Max. Stress 3.5 2.6 0.2% Proof Stress 2. 5 1. 8

Creep tests Fatigue-Endurance rotating cantilever (based on 40 million reversals) Alloy A, Alloy 13, Tons per sq. Tonsper sq. in. in.

Temperature 20 C +10. 5 +9. 5 Temperature 200 0.----- =F6. 9 =F6. 1 Temperature 300 G $4. 2 =F3. 5 Temperature 350 0 =F2. 2 =Fl.8

The fatigue figures on Alloy A were characterized by a remarkable consistency in results.

Alloy A has further been tested after bein produced by the same continuous casting process The same alloy solution treated for 20 hours at 525 C. quenched in boiling water and aged for 2 hours at 250 C. gave the following results:

Tons per sq. in. Maximum stress 27.1 0.1% proof stress 20.6

That the improved results are not merely due to the method of casting is demonstrated by the following comparison. Two alloys C and D were made up within the range of composition given for alloy A and B respectively. Both alloys were cast by the semi-continuous casting process. They were then given the following heat treatment:

Heat treatment Alloy C- 2 hours at 530 C., quenched in water at 70 C., and aged for 20 hours at 200 C. Alloy 13- 2 hours at 525 C., quenched in water at 70 C., and aged for 16 hours at C.

The alloys were then forged into bar and subjected to the following tensile tests:

Tons, as herein referred to, means long tons of 2,240 lbs. each.

What We claim is:

1. A forged aluminium alloy consisting by weight of 1.8% to 2.5% copper, 1.2% to 2.0% magnesium, 0.8% to 1.5% nickel, 0.85% to 1.5% iron, the iron and nickel together not exceeding 2.75%, up to and not exceeding 0.4% silicon, 0.02% to 0.2% titanium, and the balance essentially all aluminium substantially as described, said alloy being in the condition created by its having been subjected in the order stated to direct chill casting, forging, solution heat treating at 525 to 545 C. for 2 to 30 hours, quenching, and then ageing at 170 to 250 C. for 1 to 30 hours.

2. A forged aluminium alloy consisting by weight of 1.8% to 2.5% copper, 1.2% to 2.0% magnesium, 0.8% to 1.5% nickel, 0.85% to 1.5%

iron, the iron and nickel together not exceeding 2.75%, up to and not exceeding 0.4% silicon, 0.02% to 0.2% titanium, and the balance essentially all aluminium substantially as described, said alloy being in the condition created by its having been subjected in the order stated to direct chill casting, forging, solution heat treating at 525 to 545 C. for 2 to 30 hours, quenching, and then ageing at 170 to 250 C. for 1 to 30 hours, said alloy having a tensile strength of approximately 6.5 tons per square inch after 100 hours at 300 C. and a fatigue endurance, measured by the rotating cantilever test based on 40 million reversals, of plus-and-minus approximately 4.2 tons per square inch at 300 C.

3. A forged aluminium alloy consisting by weight of 2.1% to 2.3% copper, 1.5% to 1.7% magnesium, 1.2% to 1.4% nickel, 1.0% to 1.3% iron, 0.15% to 0.2% silicon, about 0.06% titanium, and the balance essentially all aluminium substantially as described, said alloy being in REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,744,545 Hall et al Jan. 21, 1930 2,022,686 Nook, Jr Dec. 3, 1935 2,087,988 Nook, Jr July 27, 1937 2,087,989 Nook, Jr. July 27, 1937 2,381,714 Beck Aug. 7, 1945 

1. A FORGED ALUMINUIM ALLOY CONSISTING BY WEIGHT OF 1.8% TO 2.5% COPPER, 1.2% TO 2.0% MAGNESIUM, 0.8% TO 1.5% NICKEL, 0.85% TO 1.5% IRON, THE IRON AND NICKEL TOGETHER NOT EXCEEDING 2.75%, UP TO AND NOT EXCEEDING 0.4% SILICON, 0.02% TO 0.2% TITANIUM, AND THE BALANCE ESSENTIALLY ALL ALUMINIUM SUBSTANTIALLY AS DESCRIBED, SAID ALLOY BEING IN THE CONDITION CREATED BY ITS HAVING BEEN SUBJECTED IN THE ORDER STATED TO DIRECT CHILL CASTING, FORGING, SOLUTION HEAT TREATING AT 252* TO 545* C. FOR 2 TO 30 HOURS, QUENCHING, AND THEN AGEING TO 170* TO 250* C. FOR 1 TO 30 HOURS. 